Mosquitoes are undoubtedly among the most important insect vectors of human and animal pathogens. The ability of these insects to find a vertebrate host and feed on its blood is basic to their role as a vector. There are times, however, when mosquito host-seeking and blood-feeding are inhibited endogenously. This research proposal will investigate the physiology of the endogenous inhibition occurring during oogenesis that lasts until after oviposition takes place. Prior studies have demonstrated that the ovaries produce a humoral substance which initiates the release of another hormone that inhibits host-seeking. Using techniques of microsurgery, the proposed experiments will attempt to identify the site of release of the inhibitor and the control of this release. The relationships between various physiological states and host-seeking inhibition will also be examined. An understanding of the endogenous regulation of mosquito behavior would be the basis for a control program using the insect's own hormones to manipulate its behavior.